1. Field of the Invention
This invention relates to a linear drive mechanism operable to convert rotary motion to linear motion, characterized by the provision of a slip clutch arrangement between the rotary drive shaft and the rotatably-driven cable drum means, thereby to protect the mechanism from damage.
2. Brief Description of the Prior Art
In order to convert a rotational movement produced, for example, by an electric motor, a hydraulic motor or a pneumatic motor, into a linear movement, use is normally made of threaded spindles or rack and pinion arrangements as transmission elements. The disadvantage with these types of drive means is the fact that mechanical parts move on one another, which leads to wear phenomena. Furthermore, inaccuracies as a result of production tolerances have to be taken into account in designing the drive means.
It is well known in the patented prior art to utilize flexible cables or bands for connecting a rotary drive member with a linearly displaceable driven member, as shown, for example, by the Hasler U.S. Pat. No. 4,366,722, the Blount British Patent No. 2,088,987, the Kolb German Off. No. 2,431,881, and the Jakob European Application No. 672,844.
In the copending parent application Ser. No. 08/867,799 filed Jun. 3, 1997, in the name of Peter Schubert, linear drive means have been proposed for linearly moving a body, which is guided on a housing, by means of a cable drum, which is rotatably mounted on the housing and around which a cable is wound, the latter being stretched directly between the ends of the body which are opposite in the direction of movement. If the cable drum is rotated in one direction or the other, it takes the cable with it as a result of a frictional connection, which leads to a corresponding displacement of the body to which the ends of the cable are connected. The drive operates virtually without wear, since the cable on the cable drum is only wound up or unwound. As a result of this, production tolerances in the area of the cable or cable drum can no longer have a detrimental effect on the accuracy of the drive.
Since the cable is connected under tension directly between the ends of the body, there are no further drive or deflection elements above and below, the body, which leads to a relatively low overall height. The displacement travel of the body is limited only by the cable drum, which is located at the side, but this does not lead to any further problems in the case of linear drives with a small stroke.
The problem with this embodiment is that, in the event of a collision or impact of the body with, for example, a workpiece to be processed, there is the risk that the drive of the body will be damaged.
The present invention was developed to provide an improved linear drive mechanism of the type described above wherein in all the operating conditions of the linear drive, the drive device of the body is protected against damage.